With the development of information technology, the requirements of people on the performance of flat panel display are getting higher and higher. As a third generation display technology after cathode ray tube display and liquid crystal display, OLED (Organic Light-Emitting Diode) display has the advantages of low cost, wide viewing angle, low driving voltage, fast response speed, rich light-emitting color, simple preparation process, and capability of realizing large-area flexible display, and is considered one of the most promising display technologies.
As shown in FIG. 1, an OLED device may generally include an anode AN, an organic light-emitting layer EML and cathode CA. When a driving voltage is applied to the cathode CA and the anode AN, electrons and holes are injected into the organic light-emitting layer EML from the cathode CA and the anode AN respectively and are compounded to generate excitons which jump from an excitation state to a ground state to emit light. According to spin-statistics theory, the ratio of generated singlet excitons to triplet excitons is 1:3.
For a fluorescent material, the triplet excitons accounting for 75% cannot emit light due to nonradiative transition, and light emission is transition light emission dominated by the singlet excitons accounting for 25%, which means that 75% of energy is not used for light emission.
In order to overcome the shortcoming of low light-emitting efficiency of the fluorescent material, the energy of a triplet is fully utilized, and a phosphorescent material with singlet excitons and triplet excitons participating in light emission has been developed. By doping a phosphorescent material into a host material, the triplet energy of the host material is effectively transferred to a phosphorescence doped material, and the phosphorescence doped material generates phosphorescence to emit light, thereby enabling the internal quantum efficiency to reach 100% theoretically.
Although a red phosphorescent material and a green phosphorescent material with a high efficiency have been developed, there is no blue phosphorescent material that satisfies both light-emitting efficiency and reliability. Therefore, an existing OLED device usually utilizes a blue fluorescent material, which results in a lower light-emitting efficiency of a blue light-emitting device.